The answer
Baptism is a spiritual new birth. Just as humans are physically born once, they are also spiritually born once. If the person falls, he repents, which is called a new birth.
Fr. Tadros Yacoub Malaty
Fr. Tadros Yacoub Malaty · Catechism · 710
Faith Q&A › Catechism › The Rites of Holy Baptism
Why can baptism not be repeated?
Fr. Tadros Yacoub Malaty, Catechism of the Coptic Orthodox Church, Volume 1, Books 1–3. First English Edition, 2023. Published by St. George Coptic Orthodox Church, Sporting, Alexandria, and Queen St. Mary & Prince Tadros Coptic Orthodox Church, South Brunswick, NJ. Copyright © 2023. Translation and Editing: Youth of the Coptic Orthodox Church in the USA, Canada, Europe, Australia, Arabian Gulf, and Egypt.